The present invention relates to a diaphragm plunger pump. More particularly, it relates to a diaphragm plunger pump which has a housing, a feeding chamber, a plunger working chamber which in operative condition is filled with hydraulic fluid, a sealingly clamped diaphragm which separates the feeding chamber from the plunger working chamber, a plunger which is sealingly displaceable in the plunger working chamber for alternating stroke deflection of the diaphragm, a supply chamber for hydraulic fluid connected with the plunger working chamber via at least one valve, and devices for adjusting the feeding quantity.
Diaphragm plunger pumps of the above mentioned general type are known in the art. One of such diaphragm plunger pumps is disclosed, for example, in the German document DE-AS No. 1,453,579. In this diaphragm plunger pump a bore extending parallel to the cylindrical plunger working chamber is provided. It communicates via a communicating passage with the membrane chamber and is connected with the supply chamber in an axial distance from said passage. A sleeve provided with a concentric bore is axially displaceable in the above mentioned parallel bore and is sealed on its periphery by three ring seals. A sliding rod is connected with the plunger via a dead travel connection and guided in the above concentric bore for joint movement. The sliding rod releases an opening in the sleeve communicating with the communicating passage during the suction stroke shortly before the rear dead point position of the plunger and thereby connects the plunger working chamber which is filled with hydraulic fluid with a transmission housing which serves as a supply chamber and is under outer pressure.
Since the metal sliding rod which is connected with the plunger in a laterally offset manner and slides in the sleeve does not reliably seal, leakages occur in dependence upon the operating temperature, the viscosity of the hydraulic fluid, and the difference pressure between the working chamber and the supply chamber. They undesirably affect the feeding accuracy of the diaphragm pump. Moreover, three seals are needed on the sleeve which is displaceable for adjustment of the feeding stream, of which two seals are loaded dynamically by the pulsating pressure between the suction stroke and the pressure stroke.